1. Field of the Invention
The present invention relates to an ink-jet head used in an ink-jet recording apparatus for discharging ink to print on a recording medium.
2. Description of the Related Art
An ink-jet head distributes ink supplied from an ink tank to a manifold to plural pressure chambers arranged in a matrix form. Pressure is selectively given to the respective pressure chambers by an actuator unit having a sheet-like piezoelectric ceramic, so that the ink is discharged from ink discharge ports connected to the respective pressure chambers.
With respect to the arrangement of the pressure chambers in the ink-jet head, there are a one-dimensional arrangement in which for example, one or two lines are arranged in a head direction, and a two-dimensional arrangement of a matrix form along a head surface. In order to achieve high resolution and high speed of printing requested in recent years, it is more effective to arrange the pressure chambers two-dimensionally. As an example of an ink-jet head in which pressure chambers are arranged two-dimensionally along the surface, there is known one in which a nozzle is arranged at the center of the pressure chamber when viewed in a direction vertical to a head surface (see Japanese Patent No. 3231786). In this case, when a pulse-like pressure is given to the pressure chamber, a pressure wave is transmitted in the pressure chamber in the direction vertical to the head surface, and ink is discharged from the nozzle arranged at the center of the pressure chamber when viewed in the direction vertical to the head surface.
However, in the ink-jet head disclosed in Japanese Patent No. 3231786, replenishing guide holes (ink supply ports) formed at the center of a branch duct (sub-manifold) branching from a supply duct (manifold) are communicated with a passage, and ink is supplied into the pressure chamber. In the case where air bubbles exist in the branch duct, even if an attempt is made to eject the air bubbles from the branch duct through the replenishing guide hole by a purge operation, since the replenishing guide holes are discretely provided only at the center of the branch duct, there is a possibility that hard-to move air bubbles existing at both side end upper angle parts in the width direction in the branch duct and being in contact with the inner surface of the branch duct at two points can not be ejected. That is, when an air bubble is in contact with the inner surface of the branch duct at two points, the air bubble has large contact resistance to the wall surface of the branch duct and can not be smoothly moved in the branch duct, and therefore, there occurs a possibility that the air bubble can not be ejected to the outside through the nozzle from the replenishing guide hole provided only at the center of the branch duct.